Stem cells hold promise for treatment of a number of disease states such as Parkinson's, Alzheimer's, spinal cord injury, diabetes, ischemia stroke and heart disease since stem cells have the potential under certain physiological conditions to develop into many different specialized cell types with individual functions. There are 2,620 clinical trials involving stem cells that are either on-going or have been completed, however, to-date, no stem cell therapy has received full FDA approval. The potential that stem cells offer remains to be better understood by observing their fate in vivo (e.g. bio-distribution, survival and differentiation) and this requires the means by which to track the cells non-invasively overtime. Methods are available to visualize cells, each having its own advantages and disadvantages, however, at present, no single imaging modality possess all the desired qualities for optimal evaluation of stem cell therapies. Likewise, many currently available direct cell labels have limitations due to cell toxicity, intracellular radiation effects, inefficient uptake and most importantly, rapid elution from the cell. We hypothesize that dual-modality imaging of stem cells using a non-diffusable dual-labeled imaging probe consisting of a far-red fluorophore and a radionuclide can provide complementary information regarding stem cell location longitudinally, thereby providing an accurate global picture of stem cell biodistribution in vivo which may lead to an improved understanding of stem cell biology and guide emerging stem cell therapies. In Phase I, MTTI will synthesize a dual modality probe for stem cell labeling comprising of three components: (i) a chelator (DTPA) for radiolabeling with 111In allowing detection by SPECT;(ii) a far red emitting fluorochrome to permit observation by optical imaging at the macro and micro-levels, and (iii) long hydrocarbon tails to provide stable non-diffusable incorporation of the probe into the plasma membrane. The probe's cytotoxicity, radiotoxicity, signal:noise, membrane retention and effect on various mouse stem cell functions will be characterized using standard in vitro assays. We expect to establish a suitable probe concentration which does not alter cell viability, proliferation or differentiation, and show that the probe is passed on to the next generation of daughter cells;but does not get incorporated into neighboring cells. Finally, utility of the probe to quantify and track stem cell distribution in vivo in a normal mouse using small animal SPECT and optical imaging systems will be evaluated. The fluorochrome present will also permit microscopic evaluation of tissue samples of interest after sacrifice. We expect to demonstrate that stem cells with the dual labeled marker will localize and accumulate in our animal model in a manner consistent with the cell type and be "visible" for several cell generations. Phase II will include studies in larger animal models, synthesis and evaluation of a dual modality probe for PET and optical imaging, commercialization of the dual probes as research tools and initiation of assembly of a data package for eventual clinical use. PUBLIC HEALTH RELEVANCE: Stem cells hold promise for the treatment of a number of disease states such as Parkinson's, Alzheimer's, spinal cord injury, diabetes, ischemia stroke and heart disease, but their true potential remains to be better understood by observing their fate in vivo. We propose to develop a dual modality label for stem cell tracking using nuclear and optical imaging modalities. This label is expected to provide a highly sensitive and accurate global picture of stem cell biodistribution longitudinally, which may lead to an improved understanding of stem cell biology, and in the future guide emerging stem cell therapies.